No. 3] PHENOMENA OF SEX-DIFFERENTIATION. 487 



as is illustrated in the difference observable between a normal 

 offspring of the same species and a hybrid. 



A conspicuous feature of the phenomena of irritability, to fol- 

 low Professor Sachs again, is that they correspond with the stim- 

 ulus neither qualitatively nor quantitatively, and it is in this very 

 fact that the essential distinction between the phenomena of irri- 

 tability and simple mechanical and physical and chemical action 

 lies. The explanation of this remarkable circumstance lies in the 

 irritable structure of the organ itself. The clearest expression 

 of the internal condition of an irritable organ may be obtained 

 by saying that its parts are in a condition of unstable equilibrium. 

 Hence any sudden change in the surrounding conditions may 

 serve to upset the equilibrium and precipitate a change, the final 

 outcome of which is that the protoplasm is bound to follow either 

 one direction or the other. As has been already stated, any 

 deviation in the constitution of the protoplasm that takes place 

 at the beginning of the life-history of the organism must extend 

 through the whole series of its cell derivatives, and hence the 

 effects of the changes in the surroundings, which may be diffi- 

 cult to detect in the early stages, become more and more dis- 

 cernible as the growth and development of the organism proceed. 

 The organisms up to a certain stage of their existence are neu- 

 tral as regards sex, as the result of experiments leads us to 

 infer. At this stage of sexual neutrality, the organism appears 

 to be potentially capable of assuming either the female or the 

 male organization. Whether it becomes the male or the female 

 is entirely due to the play of external forces. It is objectionable 

 to call this stage of neutral sexuality a stage of hermaphroditism, 

 as it has been designated by some naturalists, for hermaphro- 

 ditism implies the existence of two distinct sexual characters, 

 while neutrality implies the existence of a third but distinct 

 stage, in which any character approaching either male or female 

 is presumed to be entirely absent. 



The view that the development of two sexes implies the ex- 

 istence of two different conditions of the surroundings, holds 

 true in the development of two sexual cells, even when they 

 are developed in one and the same organism, as in some her- 

 maphroditic mollusca, in which the two sexual cells may arise 

 in one and the same alveolus of the germ-gland. The male 

 cell leads a free and a more or less migratory existence from 



